Synchronization in fmcw radar systems

ABSTRACT

The disclosure provides a radar apparatus for estimating a position and a velocity of the plurality of obstacles. The radar apparatus includes a local oscillator that generates a first signal. A first transmit unit receives the first signal from the local oscillator and generates a first transmit signal. A frequency shifter receives the first signal from the local oscillator and generates a second signal. A second transmit unit receives the second signal and generates a second transmit signal. The frequency shifter provides a frequency offset to the first signal based on a routing delay mismatch to generate the second signal such that the first transmit signal is phase coherent with the second transmit signal.

CROSS REFERENCES TO RELATED APPLICATIONS

This application claims priority from India provisional patentapplication No. 1667/CHE/2014 filed on Mar. 28, 2014 which is herebyincorporated by reference in its entirety.

TECHNICAL FIELD

The present disclosure relates to radars, and more particularly toestimating position and the velocity of one or more obstacles usingradars.

BACKGROUND

The use of radars in industrial and automotive applications is evolvingrapidly. Radars are used in many applications to detect target objectssuch as airplanes, military targets, vehicles, and pedestrians. Radarfinds use in number of applications associated with a vehicle such asadaptive cruise control, collision warning, blind spot warning, lanechange assist, parking assist and rear collision warning. Pulse radarand FMCW (Frequency Modulation Continuous Wave) radar are predominatelyused in such applications.

In a radar system, a local oscillator generates a transmit signal. Thetransmit signal is amplified and transmitted by one or more transmitunits. In an FMCW radar, a frequency of the transmit signal is variedlinearly with time. For example, the frequency of the transmit signalincreases at a constant rate from 77 GHz to 81 GHz in 100 micro-seconds.This transmit signal is referred as a ramp signal or a chirp signal. Oneor more obstacles scatters the transmit signal. The scattered signal isreceived by one or more receive units in the radar system.

A signal obtained by mixing the transmitted signal and the receivedscattered signal is termed as a beat signal. The beat signal is sampledby an analog to digital converter (ADC) and processed by a processor toestimate a distance and a velocity of the one or more obstacles. Thefrequency of the beat signal is proportional to the range (distance) ofthe one or more obstacles.

For a moving obstacle, a phase of the beat signal varies across multipleramp signals transmitted by the radar system. The frequency and phase ofthe beat signal from one or more receive units are analyzed by theprocessor to estimate the position and the velocity of the one or moreobstacles.

The transmit signal from the local oscillator is provided to the one ormore transmit units, and the one or more receiver units, which may be onone or multiple chips and/or semiconductor devices. The multipletransmit units and the multiple receive unit are required forbeamforming. Beamforming requires signals transmitted by the multipletransmit units to be phase coherent.

A phase coherence between multiple transmit units is affected by routingdelay mismatch. The one or more transmit or receive units may be locatedat different distances from the local oscillator which induces differentrouting delays in the transmit signal from the local oscillator to eachtransmit or receive unit. This routing delay mismatch causes errors inposition and velocity estimation of the one or more obstacles.

SUMMARY

According to an aspect of the disclosure, a radar apparatus is provided.The radar apparatus includes a local oscillator that generates a firstsignal. A first transmit unit receives the first signal from the localoscillator and generates a first transmit signal. A frequency shifterreceives the first signal from the local oscillator and generates asecond signal. A second transmit unit receives the second signal andgenerates a second transmit signal. The frequency shifter provides afrequency offset to the first signal based on a routing delay mismatchto generate the second signal such that the first transmit signal isphase coherent with the second transmit signal.

BRIEF DESCRIPTION OF THE VIEWS OF DRAWINGS

FIG. 1 illustrates a radar apparatus, according to an embodiment;

FIG. 2 illustrates a frequency shifter, according to an embodiment;

FIG. 3 illustrates a transmit unit, according to an embodiment;

FIG. 4 illustrates a transmit unit, according to an embodiment; and

FIG. 5 illustrates a receive unit, according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

FIG. 1 illustrates a radar apparatus 100, according to an embodiment.The radar apparatus 100 includes a local oscillator 102, a firsttransmit unit 104, a frequency shifter 106, a second transmit unit 108and a receive unit 110. In one version, the first transmit unit 104 andthe second transmit unit 108 are similar in operation. The firsttransmit unit 104 and the frequency shifter 106 are coupled to the localoscillator 102. The second transmit unit 108 is coupled to the frequencyshifter 106.

The receive unit 110 is coupled to the local oscillator 102. In oneexample, the radar apparatus 100 includes one or more transmit units. Inanother example, the radar apparatus 100 includes one or more receiveunits. In one version, the first transmit unit 104 and the secondtransmit unit 108 are integrated on a same chip. In another version, thefirst transmit unit 104 and the second transmit unit 108 are ondifferent chip. In yet another version, the receive unit 110 is on achip different from the first transmit unit 104 and the second transmitunit 108.

In an example, the radar apparatus 100 includes multiple localoscillators. The radar apparatus 100 may include one or more additionalcomponents known to those skilled in the relevant art and are notdiscussed here for simplicity of the description.

The operation of the radar apparatus 100 illustrated in FIG. 1 isexplained now. The local oscillator generates a first signal 114. In oneversion, a frequency of the first signal 114 is varied linearly withtime. For example, the frequency of the first signal 114 increases at aconstant rate from 77 GHz to 81 GHz in 100 micro-seconds. This firstsignal 114 is also referred as a ramp signal or a chirp signal. Inanother version, the first signal 114 is a ramp segment having a startfrequency and a fixed slope.

The frequency of the local oscillator 102 is one of the followingranges, but not limited to 76 GHz to 81 GHz or 18 GHz to 24 GHz. Thefrequency of the local oscillator 102, in one example, is dependent onan operating frequency band of the radar apparatus 100. The firsttransmit unit 104 receives the first signal 114 from the localoscillator 102, and generates a first transmit signal 116. The frequencyshifter 106 receives the first signal 114 from the local oscillator 102and generates a second signal 118. The second transmit unit 108 receivesthe second signal 118 from the frequency shifter 106 and generates asecond transmit signal 120.

The frequency shifter 106 provides a frequency offset to the firstsignal 114 based on a routing delay mismatch to generate the secondsignal 118. The frequency offset ensures that the first transmit signal116 is phase coherent with the second transmit signal 120. The frequencyoffset is estimated from at least one of the routing delay mismatch andthe fixed slope.

In one example, when the routing delay mismatch is ‘d’, and the fixedslope is ‘S’, the frequency offset provided by the frequency shifter 106is given as d*S/c. Further, c which represents a speed ofelectromagnetic wave varies from 1 m/s to 3×10⁸m/s depending on a PCB orchip material used for the radar apparatus 100. In one version, thefixed slope S is selected based on a farthest obstacle required to bedetected by the radar apparatus 100. In another version, the slope S isin the range of 1 MHz/micro-second to 200 MHz/micro-second.

The routing delay mismatch is estimated from a time difference between atime instant when the first signal 114 is generated by the localoscillator 102 and a time instant when the first transmit signal 116 istransmitted by the first transmit unit 104. The routing delay mismatchis also estimated from a time difference between the time instant whenthe first signal 114 is generated by the local oscillator 102 and a timeinstant when the second transmit signal 120 is transmitted by the secondtransmit unit 108.

The first transmit unit 104 amplifies the first signal 114 to generatethe first transmit signal 116. The second transmit unit 108 amplifiesthe second signal 118 to generate the second transmit signal 120. Thefirst transmit signal 116 and the second transmit signal 120 arecoherent in phase. The first transmit signal 116 and the second transmitsignal 120 are scattered by a plurality of obstacles to generate ascattered signal 124.

The scattered signal 124 is received by the receive unit 110. Thereceive unit 110 amplifies the scattered signal 124 to generate anamplified scattered signal. The amplified scattered signal is mixed withthe first signal 114 to generate an IF (intermediate frequency) signal.The IF signal is sampled in the receive unit 110 to generate a sampleddata. A position and a velocity of the plurality of obstacles isestimated from the sampled data.

In another embodiment, the frequency shifter 106 is between the receiveunit 110 and the local oscillator 102. The first signal 114 generated bythe local oscillator 102 is provided a frequency offset by the frequencyshifter 106, and a signal generated by the frequency shifter 106 isprovided to the receive unit.

Thus, the radar apparatus 100 provides compensation of routing delaymismatches by providing frequency offset. The frequency shifter 106provides that the transmit and receive units can be on one or multiplechips and/or semiconductor devices without any concern about routingdelay mismatch. Intra-chip routing delay mismatches can also becompensated using techniques discussed in connection with radarapparatus 100.

As frequency range of newly developed FMCW radar increases to a range of160 GHz, the use of beamforming is required for correct estimation ofthe position and the velocity of the plurality of obstacles. The radarapparatus 100 provides that a phase coherence between multiple transmitunits (for example, first transmit unit 104 and the second transmit unit108) is not affected by routing delay mismatch.

FIG. 2 illustrates a frequency shifter 200, according to an embodiment.The frequency shifter 200 is similar in connections and operation to thefrequency shifter 106 illustrated in FIG. 1. The frequency shifter 200is explained in connection with the radar apparatus 100. The frequencyshifter 200 includes a function generator 202, a digital to analogconverter (DAC) 204 and a mixer 208.

The function generator 202 receives a frequency offset value andgenerates a digital signal. In an example, the function generator 202receives the frequency offset value from a processor in the radarapparatus 100. In another example, the function generator 202 maintainsa look-up table of sine and cosine function values.

The DAC 204 is coupled to the function generator 202. The DAC 204generates an analog signal 206 corresponding to the digital signalreceived from the function generator 202. A mixer 208 is coupled the DAC204. The mixer 208 receives the analog signal 206 and a first signal214. The first signal 214 is similar to the first signal 114 generatedby the local oscillator 102 (illustrated in FIG. 1).

The mixer 208 multiplies the analog signal 206 and the first signal 214to generate the second signal 218. The second signal 218 is similar tothe second signal 118 generated by the frequency shifter 106 in radarapparatus 100. The second signal 218 thus generated by the mixer 208 isobtained by providing a frequency offset to the first signal 214. Thefrequency offset is defined by the frequency offset value received inthe function generator 202.

In another embodiment, the frequency shifter 200 is implemented using avariable delay line. In this method, the first signal 214 is sentthrough the variable delay line, whose delay is varied in proportion tothe frequency offset, such that a desired frequency shift is provided tothe first signal 214.

FIG. 3 illustrates a transmit unit 300, according to an embodiment. Thetransmit unit 300 is similar to the first transmit unit 104 inconnection and operation. The transmit unit 300 includes a conditioner304 that receives a first signal 302. The first signal 302 is similar tothe first signal 114 generated by the local oscillator 102 in the radarapparatus 100.

A first power amplifier 306 is coupled to the conditioner 304. In anembodiment, the transmit unit 300 does not include the conditioner 304and the first power amplifier 306 receives the first signal 302. A firsttransmit antenna unit 308 is coupled to the first power amplifier 306.The transmit unit 300 may include one or more additional componentsknown to those skilled in the relevant art and are not discussed herefor simplicity of the description.

The operation of the transmit unit 300 illustrated in FIG. 3 isexplained now. The conditioner 304 is configured to perform at least oneof a phase shift operation, a frequency multiplication and apre-amplification of the first signal 302. In an example, theconditioner 304 is configured to generate an output signal which is aninteger multiple of a frequency of the first signal 302. In one version,the integer is one of the following (but not limited to) 1, 2, 3 and 4.

The first power amplifier 306 receives the first signal 302 from theconditioner 304 and amplifies the first signal 302 to generate the firsttransmit signal. The first transmit antenna unit 308 transmits the firsttransmit signal received from the first power amplifier 306.

FIG. 4 illustrates a transmit unit 400, according to an embodiment. Thetransmit unit 400 is similar to the second transmit unit 108 inconnection and operation. The transmit unit 400 includes a conditioner404 that receives a second signal 402. The second signal 402 is similarto the second signal 118 generated by the frequency shifter 106 in theradar apparatus 100.

A second power amplifier 406 is coupled to the conditioner 404. In anembodiment, the transmit unit 400 does not include the conditioner 404and the second power amplifier 406 receives the second signal 402. Asecond transmit antenna unit 408 is coupled to the second poweramplifier 406. The transmit unit 400 may include one or more additionalcomponents known to those skilled in the relevant art and are notdiscussed here for simplicity of the description.

The operation of the transmit unit 400 illustrated in FIG. 4 isexplained now. The conditioner 404 is configured to perform at least oneof a phase shift operation, a frequency multiplication and apre-amplification of the second signal 402. In an example, theconditioner 404 is configured to generate an output signal which is aninteger multiple of a frequency of the second signal 402. In oneversion, the integer is one of the following (but not limited to) 1, 2,3 and 4.

The second power amplifier 406 receives the second signal 402 from theconditioner 404 and amplifies the second signal 402 to generate thesecond transmit signal. The second transmit antenna unit 408 transmitsthe second transmit signal received from the second power amplifier 406.

In one example, a routing delay between the second power amplifier 406and the second transmit antenna unit 408 is greater than a routing delaybetween the first power amplifier 306 and the first transmit antennaunit 308. This introduces routing delay mismatch in the radar apparatus100. The radar apparatus 100 provides compensation of routing delaymismatches by providing frequency offset using the frequency shifter106.

FIG. 5 illustrates a receive unit 500, according to an embodiment. Thereceive unit 500 is similar to the receive unit 110 in the radarapparatus 100. The receive unit 500 includes a receive antenna unit 502.A low-noise amplifier (LNA) 504 is coupled to the receive antenna unit502. A mixer 506 is coupled to the LNA 504 and also receives a firstsignal 508. The first signal 508 is similar to the first signal 114generated by the local oscillator 102 in the radar apparatus 100.

In one example, a multiplier receives the first signal 508 and providesthe first signal 508 to the mixer 506. A baseband filter 510 is coupledto the mixer 506. An ADC 512 is coupled to the baseband filter 510. Inan embodiment, the baseband filter 510 is not present in the receiveunit 500 and the ADC 512 is coupled to the mixer 506. A processor 514 iscoupled to the ADC 512. The receive unit 500 may include one or moreadditional components known to those skilled in the relevant art and arenot discussed here for simplicity of the description.

The operation of the receive unit 500 illustrated in FIG. 5 is explainednow. In radar apparatus 100, the first transmit signal 116 and thesecond transmit signal 120 are scattered by a plurality of obstacles togenerate a scattered signal. The receive antenna unit 502 receives thescattered signal. The LNA 504 amplifies the scattered signal to generatean amplified scattered signal.

The mixer 506 mixes the amplified scattered signal from the LNA 504 andthe first signal 508 to generate an intermediate frequency (IF) signal.In one example, the first signal 508 is received through a conditionerwhich is configured to amplify and filter the first signal 508. Thebaseband filter 510 filters the IF signal.

The ADC 512 receives the IF signal and samples the IF signal to generatea sampled data. The processor 514 receives the sampled data from the ADC512 and estimates a position and a velocity of the plurality ofobstacles from the sampled data. In an example, in the radar apparatus100, the processor 514 is coupled to the frequency shifter 106. Theprocessor 514 provided a frequency offset value to the frequency shifter106.

In one example, the processor 514 estimates the frequency offset from atleast one of the routing delay mismatch and a fixed slope of the firstsignal 508. In another example, the processor 514 is coupled to a localoscillator, for example the local oscillator 102 in the radar apparatus100. The processor 514 provides values of a start frequency and a fixedslope of the first signal 508 (or the first signal 114).

The foregoing description sets forth numerous specific details to conveya thorough understanding of the invention. However, it will be apparentto one skilled in the art that the invention may be practiced withoutthese specific details. Well-known features are sometimes not describedin detail in order to avoid obscuring the invention. Other variationsand embodiments are possible in light of above teachings, and it is thusintended that the scope of invention not be limited by this DetailedDescription, but only by the following Claims.

What is claimed is:
 1. A radar apparatus comprising a local oscillatorconfigured to generate a first signal; a first transmit unit configuredto receive the first signal from the local oscillator and configured togenerate a first transmit signal, a frequency shifter configured toreceive the first signal from the local oscillator and configured togenerate a second signal; and a second transmit unit configured toreceive the second signal and configured to generate a second transmitsignal, wherein the frequency shifter is configured to provide afrequency offset to the first signal based on a routing delay mismatchto generate the second signal such that the first transmit signal isphase coherent with the second transmit signal.
 2. The radar apparatusof claim 1, wherein the frequency shifter comprises: a functiongenerator configured to receive a frequency offset value and generates adigital signal; a digital to analog converter (DAC) coupled to thefunction generator and configured to generate an analog signalcorresponding to the digital signal, and a mixer configured to multiplythe analog signal and the first signal to generate the second signal. 3.The radar apparatus of claim 1, wherein the first transmit unitcomprises: a first power amplifier coupled to the local oscillator andconfigured to amplify the first signal to generate the first transmitsignal; and a first transmit antenna unit coupled to the first poweramplifier and configured to transmit the first transmit signal receivedfrom the first power amplifier.
 4. The radar apparatus of claim 1,wherein the second transmit unit comprises: a second power amplifiercoupled to the frequency shifter and configured to amplify the secondsignal to generate the second transmit signal; and a second transmitantenna unit coupled to the second power amplifier and configured totransmit the second transmit signal received from the second poweramplifier.
 5. The radar apparatus of claim 1, wherein the routing delaymismatch is estimated from a routing delay from the local oscillator tothe first transmit antenna unit, and from a routing delay from the localoscillator to the second transmit antenna unit.
 6. The radar apparatusof claim 1, wherein the first transmit signal and the second transmitsignal are scattered by a plurality of obstacles to generate a scatteredsignal.
 7. The radar apparatus of claim 1 further comprising a receiveunit, the receive unit comprising: a receive antenna unit configured toreceive the scattered signal; a low-noise amplifier (LNA) coupled to thereceive antenna unit and configured to amplify the scattered signal togenerate an amplified scattered signal; a mixer coupled to the LNA andthe local oscillator, the mixer configured to mix the amplifiedscattered signal and the first signal to generate an IF (intermediatefrequency) signal; an ADC (analog to digital converter) coupled to themixer and configured to sample the IF signal to generate a sampled data;and a processor coupled to the ADC and configured to estimate a positionand a velocity of the plurality of obstacles from the sampled data. 8.The radar apparatus of claim 1, wherein the first signal is a rampsegment having a start frequency and a fixed slope.
 9. The radarapparatus of claim 8, wherein the frequency offset is estimated from atleast one of the routing delay mismatch and the fixed slope.
 10. Amethod comprising: generating a first signal; generating a firsttransmit signal from a first signal; provide a frequency offset to thefirst signal based on a routing delay mismatch to generate a secondsignal; and generating a second transmit signal from the second signal,wherein the first transmit signal is phase coherent with the secondtransmit signal.
 11. The method of claim 10 further comprisingestimating the routing delay mismatch from a time difference between atime instant when the first signal is generated and a time instant whenthe first transmit signal is transmitted, and from a time differencebetween the time instant when the first signal is generated and a timeinstant when the second transmit signal is transmitted.
 12. The methodof claim 10 further comprising amplifying the first signal to generatethe first transmit signal, and amplifying the second signal to generatethe second transmit signal.
 13. The method of claim 10 furthercomprising scattering of the first transmit signal and the secondtransmit signal by a plurality of obstacles to generate a scatteredsignal.
 14. The method of claim 10 further comprising: amplifying thescattered signal to generate an amplified scattered signal; mixing theamplified scattered signal and the first signal to generate an IF(intermediate frequency) signal; sampling the IF signal to generate asampled data, and estimating a position and a velocity of the pluralityof obstacles from the sampled data.
 15. The method of claim 10, whereinthe first signal is a ramp segment having a start frequency and a fixedslope.
 16. The method of claim 15 further comprising estimating thefrequency offset from at least one of the routing delay mismatch and thefixed slope.